What drives facilitated diffusion across a membrane?

Facilitated diffusion is a passive transport process that occurs across cellular membranes with the assistance of membrane proteins. It relies primarily on the concentration gradient, which is the difference in the concentration of a substance across a membrane.

In facilitated diffusion, molecules move from an area of higher concentration to an area of lower concentration, which does not require energy input, making it a passive process. This movement continues until equilibrium is reached, where there is no net movement of the molecules across the membrane. This reliance on the concentration gradient distinguishes facilitated diffusion from active transport, which does require energy to move substances against their concentration gradient.

Therefore, the correct understanding of facilitated diffusion hinges on the concept of the concentration gradient, as this is the driving force behind the process.